Turbocharging an internal combustion engine can both reduce external emissions and increase the specific power output of the engine, as exhaust from the engine cylinders may be directed through a turbine and the resulting kinetic energy used to power a compressor. One example configuration integrates the exhaust manifolds leading from the engine cylinders to the turbine into the cylinder head itself, referred to as an integrated exhaust manifold.
The integrated exhaust manifold configuration may conserve heat energy from the exhaust gas, which may be transferred to the surrounding material of the cylinder head. This may in turn require cooling the cylinder head during normal engine operating conditions. In one example, liquid coolant may be circulated through chambers in the cylinder head, lowering the temperature of the cylinder head material and/or the exhaust gas exiting the exhaust manifold.
However, exhaust emission control devices, such as catalytic converters, achieve higher emission reduction after reaching a predetermined operating temperature. The inventors herein have realized that cooling the exhaust manifold with circulating liquid coolant may cool the exhaust gas and lengthen the amount of time necessary for the emission control device to reach the predetermined operating temperature following a cold-start condition. This may in turn increase engine emissions at cold start in the period of time before the emission control device has reached a predetermined operating temperature.
In one example, a method for operating an engine having a cylinder head, comprising: following light-off of an exhaust catalyst from a cold-start condition, circulating liquid coolant through a cooling jacket of the cylinder head, and at a subsequent engine-off condition, draining at least some of the liquid coolant from the cooling jacket. In this way, at a cold start condition, the cooling jacket of the cylinder head may be fully or partially filled with air, thus decreasing the amount of time needed for the exhaust catalyst to reach a light-off temperature. In another example, an engine system, comprising a cylinder head including a cooling jacket, a coolant tank coupled to the cooling jacket, and a coolant pump coupled to the cooling tank and cooling jacket, the coolant pump configured to circulate coolant during a first condition, and to drain coolant from the cooling jacket during a second condition. In this way, the cooling jacket may be filled with coolant during a first condition, and air-filled during a second condition, allowing improved control over the temperature of the cylinder head.
In another example, an engine method, comprising: draining a liquid cooling path following engine shut-down with the engine at rest and a coolant pump deactivated, cold-starting the engine from rest with the drained path and the pump still deactivated; and activating the pump after an exhaust catalyst reaches a light-off condition. In this way, liquid coolant is only circulated through the coolant path after the exhaust catalyst reaches the light-off condition.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.